1. Field of the Invention
This invention relates to a differential gear apparatus, more particularly to a differential gear apparatus adapted to couple a drive of a pinion mechanism which transmits a drive torque of an output shaft of an electrically powered motor to right and left driving wheels of a wheeled vehicle.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional differential gear apparatus for a motorcar is adapted to couple a drive of a pinion mechanism which transmits a drive torque of an output shaft of an electrically powered motor to right and left axles 5,5xe2x80x2 of right and left driving wheels of the motorcar. The conventional differential gear apparatus is shown to include a differential casing 1 and a side cover 11 that cooperate to form a space for receiving a gear member 2 which is driven by the motor. The gear member 2 has an axial hole 23 extending in an axial direction, and two elongate cavities 21 at two opposite sides of the axial hole 23, and two pin holes 22 are formed in central areas of the cavities 23 such that two pin shafts 33,33xe2x80x2 are inserted respectively therein. Two differential pinions 3,3xe2x80x2 are mounted respectively and rotatably on the pin shafts 33,33xe2x80x2 by means of two bearing members 32,32xe2x80x2. The right and left axles 5,5xe2x80x2 pass through axial holes 12,13 in the differential casing 1 and the side cover 11 and axial holes 41,41xe2x80x2 in two bevel wheels 4,4xe2x80x2. The right axle 5 has an inner end 53 journalled in the axial hole 23 in the gear member 2. The bevel wheels 4,4xe2x80x2 are mounted on and are rotatable with the right and left axles 5,5xe2x80x2 via two pins 52,52xe2x80x2 that pass through holes 51,51xe2x80x2 formed in the right and left axles 5,5xe2x80x2 and engage pin slots 42 of the bevel wheels 4,4xe2x80x2, and meshwith the differential pinions 3,3xe2x80x2.
With reference to FIG. 3, since the differential pinions 3,3xe2x80x2 are positioned in the cavities 21 by the pin shafts 33,33xe2x80x2 which are retained in the pin holes 22, they tend to move in the axial direction (indicated by the arrow (B)), thereby resulting in unsteady transmission thereof. When the right and left axles 5,5xe2x80x2 are positioned offset from a central axis, indicated by the arrow (A), or when there is a clearance between the differential pinions 3, 3xe2x80x2 and the bevel wheels 4,4xe2x80x2, the transmission of the differential gear apparatus will be unsteady and results in a relatively loud noise. In addition, when one element thereof, such as the bevel wheel 4, is to be replaced, it is necessary to separate all elements of the conventional differential gear apparatus from one another, thereby resulting in inconvenience.
The object of the present invention is to provide a differential gear apparatus which is capable of overcoming the aforesaid drawbacks.
According to this invention, the differential gear apparatus includes a differential casing having an outer annular wall which defines a first axis and which is provided with right and left annular ends opposite to each other in a first axial direction parallel to the first axis, and right and left walls which respectively extend from the right and left annular ends in a first direction transverse to the first axial direction. The right wall has a bearing surface which is located in a central area thereof and which extends along the first axis and towards the left wall, and front and rear cavities which are disposed at two opposite sides of the bearing surface and which extend respectively in a first longitudinal direction that is parallel to the first axial direction and towards the left wall. The front and rear cavities further extend respectively in a second transverse direction that is transverse to both the first longitudinal direction and the first transverse direction so as to form front and rear inner walls. The front and rear inner walls are spaced apart from each other in the first transverse direction and face the bearing surface. The outer annular wall of the differential casing has first and second radially extending holes which are aligned diametrically and which communicate respectively with the front and rear cavities. Front and rear shafts are respectively disposed to be fitted in the first and second radially extending holes such that each of the front and rear shafts extends into a respective one of the front and rear cavities while disposed radially and inwardly of the outer annular wall. Front and rear differential pinions are mounted respectively and rotatably on the front and rear shafts. A right axle has a right inner end journalled on the bearing surface and rotatable with the differential casing about the first axis, and a right outer end adapted to be rotated with the right driving wheel. A right bevel wheel is mounted on and is rotatable with the right axle, and meshes with both of the front and rear differential pinions. A left bevel wheel is spaced apart from the right bevel wheel in the first axial direction, and is mounted on and is rotatable with the left wall of the differential casing. The left bevel wheel is adapted to be rotated with the left driving wheel about the first axis, and meshes with the front and rear differential pinions. A ring gear member has an outer toothed rim portion adapted to engage and be driven by the pinion mechanism, and an inner rim portion opposite to the outer toothed rimportion radially, and of such a dimension as to be fittingly sleeved on the outer annular wall of the differential casing. A fastening member is disposed to releasably secure the ring gear member to the differential casing in the first axial direction so as to inhibit rotating movement of the ring gear member relative to the differential casing about the first axis.